Sheet metal forming systems and processes are commonly used to fabricate parts and members that can be used to construct and/or assemble various structures. U.S. Pat. No. 5,337,592 to Paulson discloses a roll forming process that includes a plurality of sets of non-axisymmetrical rollers serially positioned and configured to bend sheet material in a plurality of directions (e.g., longitudinally, lateral, transverse). The resulting corrugated member is a longitudinally cyclically variable cross-section member having multiple folds and bends. U.S. Pat. No. 5,489,463 to Paulson discloses a similar roll forming process that is used to form a complex member having numerous bends in different directions.
This and all other extrinsic materials discussed herein are incorporated by reference in their entirety. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
Other roll forming processes are disclosed in U.S. Pat. Nos. 317,868, 899,817, 1,677,031, 2,007,284, 2,251,967, 2,294,324, 2,471,490, 2,505,241, 2,664,177, 2,781,877, 3,137,922, 3,344,641, 3,462,989, 3,992,162, 4,220,423, 4,526,024, 4,578,978, 4,662,734, and 4876837.
The Paulson patents teach spacing the sets of rollers at a predetermined distance apart, and driving the rollers at a predetermined speed, based on a calculation of the amount of bending and “longitudinal shortening” that occurs between each set of rollers. As used herein, the term “longitudinal shortening” refers to a change in the longitudinal dimension of the sheet material per cycle of the roll forming process, (i.e., comparison of the longitudinal length of the sheet material before and after each roll-forming step). Unfortunately, many factors can contribute to a lack of precision in the calculated longitudinal shortening. For example, the actual thickness, yield strength, stiffness and spring back characteristics of the specific sheet material being bent cause significant variation in longitudinal shortening. Other factors include machine dimensional tolerances and drive motor speed variances. Considering all these factors, the probability of each sequential roller forming station adequately aligning with the bend increment in the sheet material is most unlikely if based solely on a pre-calculated estimate of longitudinal shortening. The Paulson patents, and all other known prior art, fail to provide an active alignment system that can compensate for variations in longitudinal shortening. As used herein, the term “alignment” refers to the relational position between bends in a sheet material and a roller forming station (e.g., rollers).
U.S. Patent Application Publication No. 2011/0104512 to Rapp appreciates the fact that roll forming under pressure can cause the sheet material to stretch in the longitudinal direction. Rapp also discloses varying the speed of the rollers in order to control the amount of longitudinal stretching. However, Rapp fails to compensate for variations in longitudinal shortening in order to solve the problem of misalignment.
U.S. Pat. No. 7,677,071 to Heirich discloses a sheet material roll forming process that has a variable speed motor and a driving gear coupled with a driven gear. The driving gear and driven gear can slide out of gear from one another to create a slack loop in the sheet material. U.S. Patent Application Publication No. 2010/0263424 to Madhavan discloses using optical sensors to sense a strain in a sheet material as it passes through rollers, and adjusting the speed of the rollers as a function of the strain. Variable speed electric motors for driving rollers are also taught in U.S. Pat. Nos. 6,766,843, 7,421,947, and 7,879,174. While these references contemplate that variable speed motors can be used in roll forming, the references fail to solve alignment problems caused by variations in longitudinal shortening.
Thus, there is still a need for roll forming tools and processes that compensate for variations in longitudinal shortening caused by bending into a formed shape.